1. Field of the Invention
The present invention relates to an image capturing apparatus and a control method therefor.
2. Description of the Related Art
Image capturing apparatuses have been improved in sensitivity and expanded dynamic range, which are two conflicting demands. In order to realize these demands, Japanese Patent Laid-Open No. 10-209422 proposes a photodiode having a pinned region and a region that is not pinned (hereinafter, referred to as an “un-pinned region”). The pinned region refers to a semiconductor region whose surface is provided with a p-type semiconductor region, and has a capacitance value larger than that of the un-pinned region. Charge generated by the photodiode is first accumulated in the un-pinned region. Since the un-pinned region has a small capacitance value, incident light is measured with high sensitivity. When incident light has high illuminance, and the un-pinned region is saturated, charge is then accumulated in the pinned region. Since the pinned region has a large capacitance value, a large amount of charge can be accumulated, and incident light is measured with wide dynamic range. As shown in FIG. 16 of this document, the illuminance/voltage conversion characteristics are switched before and after the saturation of the un-pinned region. Referring to such conversion characteristics, a signal obtained from a pixel is used to determine a pixel value. Japanese Patent Laid-Open No. 2002-77737 proposes a configuration that accumulates charge in a state in which a capacitance is added to a photodiode, in order to expand the dynamic range.